A hundred-and-twenty-degree modulation method and PWM (Pulse Width Modulation) sinusoidal wave modulation method are conventionally known as methods for driving DC brushless motors. Inductor voltage obtained during non-pulse intervals (periods) is used for detecting the rotational position of a DC brushless motor based on the 120-degree modulation method of some type without using position sensors, e.g., rotary encoders, resolvers, and hall elements.
For example, Japanese Unexamined Patent Application, First Publication No. H9-266690 discloses a driving apparatus used in a sensorless DC brushless motor based on the 120-degree modulation method. In order to drive a sensorless DC brushless motor stably, the rotational position of a rotor of a DC brushless motor is measured by detecting zero cross points of inductor voltage obtained in non-pulse intervals (periods) in the driving apparatus.
In addition, Japanese Unexamined Patent Application, First Publication No. 2000-218787 discloses a DC brushless motor driven based on the 120-degree modulation method in which controlling the phase of a driving current conducted in a DC brushless motor prevents non-pulse intervals (periods) from being shortened due to a voltage spike caused by emission of magnetic energy accumulated in motor coils, thereby more stably measuring a cross-section of counter-electromotive voltage produced during the non-pulse intervals and reference voltage, i.e., the rotational position of a rotor.
Patent document 1: Japanese Unexamined Patent Application, First Publication No. H9-266690
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2002-218787